1. Field of the Invention
The present invention relates to a semiconductor process system for processing substrates to be processed such as semiconductor wafers and LCD substrates and, more particularly, to an improvement in positioning for a transfer mechanism for substrates to be processed in a semiconductor process system.
2. Description of the Related Art
In a manufacturing process for a semiconductor device such as an LSI, cleaning systems are used to remove contaminants such as particles, organic contaminants, and metal impurities on a semiconductor wafer surface. Of these systems, a wet cleaning system is widely used because it can effectively remove particles and allows a batch process.
The wet cleaning system includes an input mechanism, a wafer convey robot, a plurality of process sections, and an output mechanism. The input mechanism receives a predetermined number of (e.g., 25) wafers stored in a cassette. The convey robot conveys a predetermined number of wafers received by the input mechanism, e.g., 50 wafers, at a time. The process sections are arranged to clean the wafers conveyed by the wafer convey robot all together. The output mechanism discharges the wafers cleaned by the process sections while the wafers are stored in cassettes.
The convey robot has a handler called a wafer chuck for grasping a predetermined number of wafers, e.g., 50 wafers, at once to convey them to the respective process sections. The wafer chuck has a pair of arms normally protruding in substantially the horizontal direction and opposing each other. A plurality of grooves corresponding to the number of wafers to be grasped are formed in these arms at predetermined intervals. Peripheral portions of wafers are inserted in these grooves. The two arms are then brought close to each other to grasp the wafers in a vertical position.
A holder called a boat for holding wafers conveyed by the wafer chuck, i.e., the handler, is arranged in the process vessel of each process section for cleaning wafers. The boat receives and holds the wafers grasped by the handler all together. For this purpose, the boat has a plurality of grooves corresponding to the grooves of the handler, and receives and holds peripheral portions of the wafers in the grooves in a vertical position.
When, therefore, wafers are transferred between the wafer chuck, i.e., the handler, and the boat, i.e., the holder, the grooves of the handler which are designed to determine the respective grasping positions must be located on the same perpendicular planes as those of the grooves of the holder which are designed to determine the respective holding positions. Otherwise wafers cannot be smoothly transferred. For this reason, positioning between the handler and the holder must be performed in advance. Since the holder is generally fixed in each process vessel, positioning is performed by properly adjusting/moving the handler in the X and Y directions.
In a conventional positioning method, a plurality of dummy wafers are grasped by the handler, and an operator manually adjusts the setting position of the handler properly while carefully observing the positional relationship between peripheral portions of the dummy wafers and corresponding grooves of the holder, thereby properly inserting the peripheral portions of the dummy wafers into the corresponding grooves of the holder in vertical states. This method, however, greatly depends on the skill of each operator, and the possibility of human error cannot be denied. That is, the method lacks reliability. In addition, the operator must check the actual state of transfer of wafers in each process vessel by directly looking into the vessel. For this reason, the working environment is poor, and it takes much time and labor to adjust the handler.
In another conventional positioning method, a position where the handler transfers wafers is accurately measured in advance to be determined as a reference position, and the position of the handler is detected by a distance sensor. The difference between the reference and detected positions of the handler is displayed in numerical values, thus detecting a positional offset. The setting position of the handler is properly adjusted to nullify the difference. In this method, however, an error tends to occur in actual measurement for determining the reference position of the handler. That is, similar to the above case of manual operation, the method lacks reliability. Furthermore, since the shape of the handler is not simple, distance sensors need to be set in a large number of places to detect the position of the handler. As a result, the positioning mechanism itself is complicated. In addition, since such sensors must be arranged in each process vessel, new problems are posed in terms of resistance to a cleaning solution and water tightness.